Organic Chapter 2: Alkanes & Halogenoalkanes

Question 1

What is the General Formula for an alkane?

Answer 1

C_nH_2n+2

Question 2

What is an alkane?

Answer 2

A saturated hydrocarbon

Question 3

What is the general formula for a Cycloalkane?

Answer 3

C_nH_2n

Question 4

What is Crude Oil mostly made up of?

Answer 4

Alkanes

Question 5

Why do we separate Crude Oil?

Answer 5

It’s not very useful in raw form

Question 6

How do we separate Crude Oil?

Answer 6

Fractional Distillation

Question 7

How does Fractional Distillation work?

Answer 7

Crude Oil is vaporised at around 350 degrees C
Vaporised Crude Oil goes to the top of the fractioning column
Crude Oil vapour gets cooler as it goes up the column
Each different chemical condenses at a different temperature - liquids get filtered off
Hydrocarbons with lowest & highest bp are taken at the top & bottom of the column respectively

Question 8

How can you separate long chain hydrocarbons?

Answer 8

Cracking

Question 9

What are the two types of Cracking?

Answer 9

Thermal Cracking
Catalytic Cracking

Question 10

What are the conditions for Thermal Cracking? What does it mainly produce?

Answer 10

High pressure & High temp (up to 70atm & 1000 degrees C)
Produces a lot of alkenes

Question 11

What are the conditions for Catalytic cracking? What does it mainly produce?

Answer 11

Takes place in the prescence of a Zeolite Catalyst at a slight pressure & high temperature (450 degrees)
Mostly produces aromatic compounds
Catalytic cracking is cheaper and faster.

Question 12

What are alkanes useful for?

Answer 12

Fuels

Question 13

What causes incomplete combustion?

Answer 13

Lack of oxygen

Question 14

What is the equation for incomplete combustion of methane?

Answer 14

2CH₄ + 3O₂ -> 2CO + 4H₂O

Question 15

Why does burning fossil fuels contribute to global warming?

Answer 15

It produces carbon dioxide - this is a greenhouse gas.

Question 16

What do Catalytic converters do on cars?

Answer 16

Remove unburnt hydrocarbons & oxides of nitrogen from the exhaust

Question 17

What causes acid rain?

Answer 17

Sulfur Dioxide

Question 18

What is a Free Radical?

Answer 18

A particle with an unpaired electron

Question 19

What causes free radicals to form?

Answer 19

When a covalent bond splits equally - both atoms get 1 of the shared electrons

Question 20

What is special about free radicals?

Answer 20

They’re very reactive due to the single unpaired electron

Question 21

How do you indicate a free radical?

Answer 21

Dot next to the chemical

e.g Cl^.

Question 22

What is an initiation step?

Answer 22

A step in a reaction where free radicals are produced

Question 23

What is a propagation step?

Answer 23

Free radicals are both used up & created

Question 24

What is a termination step?

Answer 24

Free radicals are completely used up

Question 25

Why are CFCs now banned?

Answer 25

Because they produced chlorine free radicals and caused ozone layer damage

Question 26

What is the equation for chlorine free radicals breaking down the ozone layer?

Answer 26

Overall: 2O₃ -> 3O₂ Cl₂ -> 2Cl^. Cl^. + O₃ -> O₂ + ClO^. ClO^. + O₃ -> 2O₂ + Cl^. 2Cl^. -> Cl₂

Question 27

Under what conditions do free radicals form?

Answer 27

Prescence of UV light

Question 28

What is a Halogenoalkane?

Answer 28

An alkane with a halogen atom on it

Question 29

What is special about the carbon-halogen bond in a halogenoalkane?

Answer 29

It's polar

Question 30

What are some nucleophiles that can react with halogenoalkanes?

Answer 30

OH^- CN^- NH₃

Question 31

What reaction do Halogenalkanes undergo to become alcohols?

Answer 31

Nucleophilic substitution warm Aqueous sodium or potassium hydroxide

Question 32

What reaction do Halogenoalkanes undergo to become Nitriles?

Answer 32

Nucleophilic substitution Warmed ethanolic potassium cyanide Heat under Reflux

Question 33

What reaction do Halogenoalkanes undergo to become Amines?

Answer 33

Nucleophilic substitution Excess Ethanolic Ammonia

Question 34

Which Halogenoalkanes react the fastest and which the slowest?

Answer 34

Iodoalkanes are the fastest Flouroalkanes are the slowest

Question 35

What reaction do halogenoalkanes undergo to become Alkenes?

Answer 35

Elimination Ethanolic hydroxide ions Heat under reflux